The present invention relates to a transmitter of a wireless tire condition monitoring apparatus that allows a driver in a vehicle passenger compartment to check the conditions such as the air pressure of the tires.
Wireless tire condition monitoring apparatuses have been proposed for allowing a driver in a vehicle passenger compartment to check the conditions of vehicle tires. Such monitoring apparatus includes transmitters and a receiver. Each transmitter is located in one of the tires and the receiver is located in the body frame of the vehicle. Each transmitter detects the conditions of the associated tire, such as the air pressure and the temperature, and wirelessly transmits the detection information. The receiver receives the information from the transmitters via an antenna provided on the receiver. The condition of each tire is then displayed, for example, on the indicator located near the driver's seat.
Since each transmitter is powered by a battery, the transmitter stops operating when the battery runs down. At such a time, each transmitter cannot detect the conditions of the corresponding tire. However, each transmitter is attached to the corresponding wheel and is located in the corresponding tire. To change the battery of a transmitter, the tire must be removed from the wheel. Changing the battery of a transmitter is therefore burdensome. Further, the transmitters are constructed with a high accuracy to be durable against the harsh condition in the tire. Therefore, opening the casing of a transmitter for changing the battery can make the transmitter less reliable. Accordingly, changing the battery is not practical.
The capacity of the battery may be increased to permit the transmitter to function for a long period without changing the battery. This, however, increases the size and the weight of the battery thus altering the balance of the corresponding tire. Therefore, the capacity of the battery cannot be increased beyond a certain limit.
Accordingly, some prior art apparatuses use transmitters that only periodically detect the tire conditions and transmit data that represents the tire condition. This minimizes the cumulative operating time of the transmitters, which allows batteries having a relatively small capacity to be used for a long period.
To extend the life of the batteries, the detection interval of each transmitter is preferably increased. However, if the detection interval is increased, the transmitter cannot inform abnormal changes in the air pressure in detail in a case when the air pressure rapidly decreases by, for example, damage. On the other hand, if the detection interval of each transmitter is relatively short, the transmitter can inform abnormal changes in the air pressure in detail. However, in this case, the cumulative operating time of the transmitters increases, thus shortening the life of the batteries. It is difficult to solve such conflicting problems.